There has been extensive research directed to the development of flame retardant thermoplastic resin compositions. Conventional methods for imparting flame retardancy to thermoplastic resins include blending the thermoplastic resin composition with a flame retardant agent, such as an antimony-containing, halogen-containing, phosphorus-containing or nitrogen-containing compound.
For example, one conventional technique for imparting flame retardancy to a thermoplastic resin includes adding a halogen-containing flame retardant and an antimony-containing compound to the resin composition. Halogen-containing flame retardants and antimony-containing compounds can impart a desired level of flame retardancy to thermoplastic resin products without significantly degrading the physical properties thereof. However, there is concern regarding the effect of hydrogen halide gases released by halogen-containing compounds during processing on the human body. In this regard, polybromodiphenyl ether, which is widely used as a halogen-containing flame retardant, may produce toxic gases such as dioxin or furan during combustion and thus can be harmful to humans and the environment. Accordingly, there is a need to develop flame retardancy methods that do not employ halogen-containing compounds.
Currently the most common method for imparting flame retardancy without using halogen-containing flame retardants uses a phosphate ester flame retardant. However, the phosphate ester flame retardant has a disadvantage in that it is necessary to add an excessive amount in order to obtain a certain level of flame retardancy.
International Publication No. WO 2004/087809 and Japanese Publication No. 2002-037973 disclose a pentaerythritol alkyl phosphonate compound and an addition type of flameproof resin employing the same. However, these documents do not disclose a method of preparing a phosphoric flameproof compound, which uses a cyanide alkyl phosphonate group derivative with a pentaerythritol compound, and a thermoplastic resin composition including the same.